A sliding gate valve for opening and closing a discharge opening formed in the bottom wall of a molten metal container is secured to the bottom of the molten metal container
A two-layer type slide gate valve unit embodying the present invention will be described with reference to FIG. 3. A base frame 2 is secured to the bottom wall of a molten metal container 1. A fixed plate 3 is combined with the base frame 2. A slide plate 5 and a shoot nozzle 6 are supported on a slide case 4 disposed under the fixed plate 3. The slide case 4 is pushed and pulled by a hydraulic or electric cylinder actuator 7 to align the nozzle hole 5a of the slide plate 5 with the nozzle hole 3a of the fixed plate 3 and to disconnect the nozzle hole 5a of the slide plate 5 from the nozzle hole 3a of the fixed plate 3. Thus the discharge of the molten metal from the molten metal container through an insert nozzle 8 is controlled. In some cases, a long nozzle or an immersion nozzle is put on the shoot nozzle 6.
The slide case 4 is pushed upward by a pressing means including a spring to press the slide plate 5 against the fixed plate 3 by a predetermined pressure to prevent the leakage of the molten metal from the respective nozzle holes 3a and 5a of the plates 3 and 5 and the penetration of air into the molten metal.
The pressing means of the slide gate valve unit of such basic construction is a spring means disclosed in, for example, Patent document 1.
In the known spring means, a lower pin extending upward so as to penetrate a casing frame supporting a slide frame and an upper pin extending downward so as to penetrate a fixed frame are connected by screwing, a compression spring is extended between the head of the upper pin and the fixed frame so as to exert the resilience of the compression spring on the head of the upper pin to pull up the lower pin. Consequently, the casing frame supporting the slide case is pulled up by the lower pin to press the slide plate against the fixed plate by a predetermined pressure.
This known pressing means uses the two pins. The two pins need to be connected by screwing after being extended through the casing frame and the fixed plate, respectively. Thus this known pressing means needs troublesome assembling work and many parts, the pins having strength sufficient to pull up the slide case need to be thick ones, the compression spring necessarily has a big outside diameter, and hence the pressing means needs a large space for installation.
The casing frame is fastened to the base frame with bolts. Therefore the casing frame is irregularly joined to the base frame and it is difficult to press the sliding surface of the slide plate uniformly against the sliding surface of the fixed plate, which is undesirable from the viewpoint of preventing the leakage of the molten metal and the penetration of air into the molten metal.
Patent document 1: JP 1-38592 B